Advertising Generic Information in IS-IS

1
Advertising Generic Information in IS-IS

• draft-ginsberg-isis-genapp-00.txt
• Les Ginsberg
• Stefano Previdi
• Mike Shand

2
Use of TLV Codepoints

• Number of TLV codepoints is limited to 256
• Currently 37 have been assigned
• Application Advertisements Could Consume this
  space

3
Use of sub-TLVs

• Use of sub-TLVs (introduced by RFC 3784) provides
  additional codepoints within the context of the
  parent TLV
• Multiple levels of sub-TLVs are allowed but
  create encoding inefficiency
• Encoding inefficiency increases the likelihood
  that a single TLV (255 octets) will be
  insufficient to describe all attributes for an
  object

4
GENAPP Solution

• Assign one TLV for use by all applications
• Define an Application ID to provide a unique
  context for each application
• Each application has 256 sub-TLV codepoints
• No additional TLV codepoints required ever!!
• Minimizes need for nested sub-TLVs
• Can be advertised only in LSPs not IIHs/SNPs

5
TLV Format
Type 251 (proposed) Length of octets in the
value field (3 to 255) Value
No. of octets
-----------------------------
Flags 1
-----------------------------
Application ID 2
-----------------------------
Application
IP Address Info 0 to 20
-----------------------------
Additional Application 0 to (252 -
Specific Information len of
IP Address info) ------------------
-----------
6
Field Description
0 1 2 3 4 5 6 7 --------
Rsvd VIDS Flags -------- S
Domain wide flooding D Down bit I IPv4
address follows V- IPv6 address
follows Application ID assigned by
IANA Application IP Address Info IPv4 and/or
IPv6 address for application (not necessarily a
Router ID)
7
Flooding Procedures

• Each GENAPP TLV describes exactly one application
• Information with different flooding scopes
  requires different TLVs
• S-bit gt domain-wide flooding
• D-bit set indicates L2-gtL1 leaking has occurred
  do NOT leak back into L2
• Do NOT use information in the LSP of an
  unreachable system could be stale
• Updates SHOULD be advertised in the same LSP
  whenever possible

8
Use with Caution

• Sending additional information has the potential
  to negatively impact performance of the protocol
• DAMPENING MUST BE DONE!!

9
Relationship to Router Capabilities

• draft-ietf-isis-caps-06.txt
• Reserved for router capabilities (not
  applications)
• Format is not as flexible (all sub-TLVs share
  same context)
• Same flooding rules

10

• WG Item???